A saturated fluorohydrocarbon gas having 3 to 5 carbon atoms may be used as an etching gas (see Patent Documents 1 to 3).
For example, Patent Document 1 discloses a saturated fluorohydrocarbon represented by CxHyFz (wherein x is 3, 4, or 5, and y and z are independently a positive integer, provided that y>z is satisfied) as a gas that is used to selectively etch a silicon nitride film when etching a silicon nitride film that covers a silicon oxide film. In the examples of Patent Document 1, only a silicon nitride film is selectively etched at a rate of 64 nm/min (selectivity ratio: infinity) using 2,2-difluoro-n-butane without etching a silicon oxide film.
Patent Document 2 considers that C3H5F3 gas (i.e., one of the saturated fluorohydrocarbons disclosed in Patent Document 1) may be used as an etching gas that achieves a high selectivity ratio (see paragraph 0106). This is because a reaction product is deposited on a mask, and the etching target area is etched.
Patent Document 3 discloses that C3H7F and C3H6F2 function as a protective film-forming substance during etching when used in combination with another etching gas such as C4F6 gas or oxygen.
Patent Document 4 discloses that a contact hole having a high aspect ratio can be formed by selectively etching a silicon oxide film, a silicon nitride film, or the like relative to a resist or silicon using a dry etching gas that includes an unsaturated perfluorocarbon (see paragraph 0004).
Several etching techniques that selectively etch a silicon nitride film or the like relative to a silicon oxide film, a silicon film, or the like have been proposed as described above.
However, development of a technique that can more selectively etch a silicon nitride film relative to a silicon oxide film, a silicon film, or the like without damaging another film (particularly a silicon film or a silicon oxide film) has been desired along with the recent development of semiconductor production technology.